CVE-2026-81686 in openssl_encrypt
Summary
by MITRE • 08/27/2026
openssl_encrypt 1.4.x before 1.4.9 contains an optional D-Bus crypto service whose org.freedesktop.DBus.Properties.Set method performs neither a polkit authorization check nor value validation. Any local user on the system bus can call Set without authorization and set MaxConcurrentOperations (to 0/negative, causing the concurrency gate to refuse all subsequent operations, or to a huge value removing the limit) or the unbounded DefaultTimeout, resulting in a persistent denial of service of the root daemon. The D-Bus service exists only on the 1.4.x line and was removed in 1.5.x.
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Analysis
by VulDB Data Team • 08/27/2026
The vulnerability identified within openssl_encrypt versions prior to 1.4.9 stems from an insecure configuration of a privileged D-Bus crypto service, specifically involving the org.freedesktop.DBus.Properties.Set method. This interface is designed to allow modification of properties governing the behavior of a root-level daemon responsible for cryptographic operations. However, the implementation fails to enforce polkit authorization checks and lacks any form of input validation on the values being set by callers. In typical Linux systems utilizing D-Bus as an inter-process communication bus, local users can send messages to system-wide services unless explicit access control policies are in place. The absence of these safeguards means that any unprivileged user with access to the system bus can interact directly with this sensitive service without authentication or authorization, effectively bypassing standard security boundaries intended to protect root-level processes from unauthorized manipulation by lower-privilege entities.
The technical flaw centers on two critical properties: MaxConcurrentOperations and DefaultTimeout. The MaxConcurrentOperations parameter dictates how many cryptographic operations the daemon can process simultaneously before applying a concurrency gate that throttles or rejects further requests. By setting this value to zero or a negative number, an attacker causes the service to refuse all subsequent operations entirely, effectively freezing the functionality of the crypto daemon for legitimate users and applications relying on it. Alternatively, by setting MaxConcurrentOperations to an excessively large integer, the concurrency limit is removed, potentially leading to resource exhaustion as the system attempts to handle an unbounded number of parallel cryptographic tasks, consuming excessive CPU and memory resources until the service or entire system becomes unstable. Similarly, the DefaultTimeout property controls how long the daemon waits for operations to complete before timing out. Setting this value without bounds allows attackers to configure timeouts that are either too short, causing premature termination of legitimate requests, or excessively long, leading to resource leaks where connections and memory allocations remain open indefinitely, contributing further to denial-of-service conditions through resource starvation.
The operational impact of this vulnerability is a persistent and reliable local denial of service against the root daemon managing cryptographic services. Because the flaw allows any local user to disrupt the service without detection or prevention mechanisms in place by default, it represents a significant availability risk for systems relying on these crypto functions for authentication, encryption at rest, secure communications, or other security-critical tasks. The impact is particularly severe because the affected component operates with root privileges; while the attacker does not gain direct code execution rights through this specific flaw, they can effectively cripple essential system services required by multiple applications and users. This type of availability compromise aligns closely with CWE-787: Out-of-bounds Write in terms of resource management failure, though more accurately it maps to CWE-400: Uncontrolled Resource Consumption when the concurrency limit is removed, or CWE-253: Check for Correctness before Performing Operation if considering the lack of validation. From an adversarial perspective, this behavior corresponds to ATT&CK technique T1496: Resource Hijacking, where attackers consume system resources to degrade performance and availability rather than stealing data directly.
Mitigation strategies primarily involve upgrading to openssl_encrypt version 1.4.9 or later, as the problematic D-Bus service was entirely removed in the 1.5.x branch of the software, eliminating the attack surface associated with this specific interface. For systems that cannot immediately upgrade due to compatibility constraints, administrators should implement strict polkit rules to restrict access to the org.freedesktop.DBus.Properties.Set method on the affected crypto service bus name to only authorized users or groups. Additionally, configuring D-Bus security policies via systemd socket activation or direct dbus-daemon configuration files can enforce authentication requirements for system bus interactions involving privileged services. Input validation should also be enforced at the application level if any custom wrappers exist around these calls, ensuring that numeric parameters fall within expected ranges and preventing extreme values from being accepted by the daemon logic. Regular auditing of D-Bus service configurations against industry best practices such as those outlined in CIS Benchmarks for Linux can help identify similar misconfigurations across other privileged services running on the system bus.